Silphos [PCl3-n(SiO2)n]: A heterogeneous phosphine reagent for the conversion of epoxides to β-bromoformates or alkenes

Article abstract of DOI:10.1016/j.tet.2005.11.042

Silphos [PCl_3-n(SiO₂)_n] as a heterogeneous phosphine reagent is efficiently applied for the transformation of epoxides to β-bromoformates in the presence of bromine or N-bromosuccinimide in dimethyl formamide at 0 °C. The combination of Silphos and iodine was also found suitable for the room temperature preparation of alkenes. The use of Silphos provides the advantage of easy separation of the phosphine oxide by-product from the reaction mixture.

Full text of DOI:10.1016/j.tet.2005.11.042

Tetrahedron 62 (2006) 1823–1827
Silphos [PCl3Kn(SiO2)n]: a heterogeneous phosphine reagent for
the conversion of epoxides to b-bromoformates or alkenes
* *
Nasser Iranpoor, Habib Firouzabadi and Arezu Jamalian
Department of Chemistry, College of Sciences, Shiraz University, Shiraz 71454, Iran
Received 3 October 2005; revised 2 November 2005; accepted 17 November 2005
Available online 13 December 2005
Abstract—Silphos [PCl3Kn(SiO2)n] as a heterogeneous phosphine reagent is efficiently applied for the transformation of epoxides to
b-bromoformates in the presence of bromine or N-bromosuccinimide in dimethyl formamide at 0 8C. The combination of Silphos and iodine
was also found suitable for the room temperature preparation of alkenes. The use of Silphos provides the advantage of easy separation of the
phosphine oxide by-product from the reaction mixture.
q 2006 Published by Elsevier Ltd.
1. Introduction
the recently reported examples of the useful phosphines,
which are not easily prepared and available reagents.
Epoxides, as strained three-membered heterocyclic inter-
mediates, play an increasingly important role in organic
synthesis1 and their nucleophilic ring opening reactions
under mild conditions are of great interest.2–4 On the other
hand, synthetic transformation of different functionalities by
using the combination of PPh3 and molecular halogens or
reagents carrying electrophilic halogens have been widely
investigated.5,6 It has been reported that applying these
reagents in dry DMF provides a useful method for the
formylation of hydroxyl groups.7,8 We have also applied
PPh3/Br2 or PPh3/NBS in DMF for the synthesis of
b-bromoformates from epoxides.9 Despite the novelty of
the reported method, this procedure along with other
synthetic methods using homogeneous phosphine reagents
as oxophile, have a common limitation, which is the
formation of stoichiometric amount of phosphine oxide by-
product in which its separation from the reaction mixture is
usually a difficult task and requires time consuming
techniques. As a solution to this problem, various
heterogeneous or polymeric supported phosphine reagents
have been presented and used for different synthetic
purposes. Polystyrene supported triphenylphosphine,10
ROMPgel-supported triphenylphosphine,11 4-diphenyl-
phosphanyl-benzoic acid 2-trimethylsilanyl ethyl ester,12
non-cross-linked polystyrene triphenylphosphine13 and
polymer-supported triphenylphosphine resin14 are some of
Recently, we have introduced a cheap and easily prepared
heterogeneous phosphine reagent, Silphos [PCl3Kn(SiO2)n],
and used it for bromination and iodination of alcohols and
thiols,15 deoxygenation of sulfoxides, reductive coupling of
sulfonyl chlorides16 and formylation and acetylation of
alcohols and amines.17 Now, we report on the ability of this
reagent for the synthesis of b-bromoformates from epoxides
in the presence of Br2 or NBS at 0 8C in DMF (Fig. 1).
Silphos/Br2 or NBS
PhO
Br
DMF, 0oC
OCHO
PhO
Silphos/I2
DMF, rt
O
PhO
Silphos=PCl3-n(SiO2)n
Figure 1. Conversion of epoxides to their corresponding b-bromoformates
and alkenes in the presence of Silphos [PCl3Kn(SiO2)n] and halogenating
agents.
The reaction of 2,3-epoxypropylphenyl ether with different
ratios of N-bromosuccinimide (NBS), Br2 and I2 in
combination with Silphos [PCl3Kn(SiO2)n] in dry DMF were
studied. The data are summarized in Table 1. As shown, in the
presence of 1.5 g of Silphos, the ratio of 1.2 for Br2/epoxide
was sufficient to complete the reaction. However, under this
condition, a mixture of products (b-bromohydrin, b-bromo-
formate, and alkene) was produced (Table 1, entry 2).
Increasing the amount of bromine did not show any
considerable difference in the distribution of the products
obtained. Refluxing the reaction mixture favoured the
formation of alkene over bromoformate (Table 1, entry 4).
Keywords: Silphos; Heterogeneous phosphine reagent; Epoxides; b-
Bromoformates; Alkenes.
*
Corresponding authors. Tel.: C98 711 2287600; fax: C98 711 2280926;
e-mail addresses: iranpoor@chem.susc.ac.ir; firouzabadi@chem.
susc.ac.ir
0040–4020/$ - see front matter q 2006 Published by Elsevier Ltd.
doi:10.1016/j.tet.2005.11.042

1824
N. Iranpoor et al. / Tetrahedron 62 (2006) 1823–1827
Table 1. Reactions of 2,3-epoxypropylphenyl ether with 1.5 g of Silphos [PCl3Kn(SiO2)n] and different ratios of Br2, NBS or 1.0 g of Silphos in the presence of
different mmol of molecular iodine
Entry
Reagent
Substrate/reagent
Reaction temperature
Time (h)
Conversion (%)
1
2
3
4
5
6
7
8
Br2
Br2
Br2
Br2
Br2
NBS
I2
1:1
rt
rt
rt
5
3
1
0.3
1
3.5
80a
100a
100a
100b
100
1:1.2
1:1.4
1:1.4
1:1.4
1:1.4
1:1.8
1:2
Reflux
0 8C
0 8C
rt
100
80c
1
I2
rt
!10 min
100d
a Mixture of bromohydrin, bromoformate and alkene was produced in almost equal amounts.
b The amount of produced alkene was w45%.
c The products were found to be iodohydrine and alkene with the ratio of 30:70 by NMR analysis.
d Conversion to 3-phenoxy propene was observed.
The best reaction condition was obtained when the reaction
mixture was cooled down to 0 8C, in which 2,3-epoxypropyl-
phenyl ether was quantitatively converted to its corresponding
b-bromoformatein1 h(Table1,entry5).Replacingmolecular
bromine with NBS required more reaction time (w3.5 h) for
the above transformation (Table 1, entry 6). In this study, it
was also observed that increasing the molar ratio of molecular
iodine up to 2, converts 2,3-epoxypropylphenyl ether
quantitatively to 3-phenoxy propene (Table 1, entry 8).
Applying 1.5 g of Silphos with 1.4 mmol of bromine or
NBS to 1.0 mmol of different epoxides in dry DMF
yielded the corresponding b-bromoformates (Table 2).
The results show that epoxides carrying either electron-
donating or withdrawing groups reacts under these
conditions and yields the corresponding b-bromoformates
in good to high yields. For entries 8 and 9 of Table 2,
the conversion was not complete and a mixture of
unidentified products was observed.
Table 2. Conversion of epoxides to b-bromoformates in the presence of 1.5 g of Silphos [PCl3Kn(SiO2)n] and 1.4 mmol of Br2 or NBS in DMF at 0 8C
Entry
Substrate
Silphos/Br2
Silphos/NBS
Yield (%)
Producta
Time (min)
Yield (%)
Time (h)
O
O
O
1
2
35
40
91
92
1
3
93
90
Me2CHOCH2CH(OCHO)CH2Br
O
CH2]CHCH2OCH2CH(OCHO)CH2Br
O
3
4
5
20
60
40
85
96
88
1
90
92
85
Me(CH2)3CH(OCHO)CH2Br
PhOCH2CH(OCHO)CH2Br
ClCH2CH(OCHO)CH2Br
O
3.5
3
PhO
Cl
O
O
6
7
15
20
58
70
0.5
1
60
74
PhCH(Br)CH2OCHO
Ph
Br
O
OCHO
O
O
b
8
9
3 h
—
—
24
—
—
—
O
O
O
c
—
24 h
24
O
a For entries 1–5, a trace amount of their corresponding alkene was produced. In the case of styrene oxide, entry 6, a mixture of products, styrene (10%),
2-bromo-2-phenyl ethanol (20%) were also obtained. 2-Bromo-2-phenyl ethanol has a primary hydroxyl group and cannot be formylated.8b For entry 7,
w15% of cyclohexene and trace amount of unidentified products were produced.
b The conversion was 50% and a mixture of unidentified products was produced.
c The conversion was 40% and a mixture of unidentified products was produced.

N. Iranpoor et al. / Tetrahedron 62 (2006) 1823–1827
1825
On the basis of literature,7b,c,9 a similar mechanism is
proposed for bromformylation of epoxides with Silphos
(Fig. 2).
reported for removing oxygen from epoxides,19 which
mostly require expensive reagents, harsh reaction con-
ditions and have problems for the separation of the
phosphine oxide by-product from the reaction mixture, for
example, the use of PPh3/I2 has the problem for the isolation
of alkene from the reaction mixture and only conversion
yield is reported.9
SiO2
SiO2
O
Br
P
-
+
.
)
)
HC NMe2
PCl3-nBr2+
O
O CH=NMe2 Br
O
n
n
Cl3-n
In continuation of our study, we optimized the reaction
conditions for the conversion of epoxides to alkenes by
applying different quantities of Silphos and I2 in various
solvents such as benzene, CH2Cl2, CH3CN, and DMF at
various temperatures. We observed that in the presence of
Silphos (1.0 g) and 2.0 mmol of iodine, 1.0 mmol of
epoxide can be quantitatively converted to its alkene in
dry DMF at room temperature. Any change in the ratio of
substrate and reagents produces a mixture of products. The
results obtained from deoxygenation of structurally different
classes of epoxides by the Silphos/I2 system in dry DMF are
shown in Table 3. The advantage of using Silphos/I2 system
is that the produced alkenes can be easily isolated from the
reaction mixture.
SiO2
Br
O
-
+
-
+
+
.
.
)
O
P
O
CH=NMe2 Br +
n
O
CH=NMe2 2Br
-Silphos-oxide
Cl3-n
Br
-
+
-
+
+
.
.
O
CH=NMe2 Br
O
CH=NMe2 2Br
Br
Br
+
-
H2O
.
.
O
CHO + NHEt2 HBr
O
CH=NMe2 Br
Figure 2. Mechanism proposed for the conversion of epoxides to their
corresponding b-bromoformates in the presence of Silphos [PCl3K
n(SiO2)n].
2. Conclusion
Deoxygenation of epoxides to alkenes enables epoxides
to be introduced as protecting groups for double bonds.18
A number of methods using phosphine reagents have been
In this study, we have introduced a new application for
Silphos [PCl3Kn(SiO2)n] as a cheap, efficient and easily
Table 3. Conversion of 1.0 mmol of epoxides to their corresponding alkenes by 1.0 g of Silphos [PCl3Kn(SiO2)n] and 2.0 mmol of I2 in DMF at room
temperature
Entry
Substrate
Time (min)
Product
Yield (%)
O
O
O
1
2
5
77
88
O
O
15
O
O
3
4
5
15
80
93
74
O
PhO
Cl
!10
25
PhO
Cl
O
6
7
O
10
79
89
O
!5
Ph
Ph
O
O
O
8
3 ha
O
90
O
O
O
b
9
24 h
—
—
O
a 1.5 g of Silphos was used.
b The conversion was 50% and mixture of products was produced after 24 h in reflux condition.

1826
N. Iranpoor et al. / Tetrahedron 62 (2006) 1823–1827
prepared heterogeneous phosphine reagent for the conver-
sion of epoxides to their corresponding b-bromoformates or
alkenes. The Silphos-oxide produced from the reaction can
be removed with a filtration and offers a very simple and
practical work-up.
mixture was stirred until the complete conversion of the
epoxide to alkenes. The reaction mixture was then filtered to
separate the Silphos-oxide. The filtrate was poured into
saturated brine and the product was extracted by 2!30 mL
of ether. The organic layer was washed with 2!20 mL of an
aqueous solution of 10% sodium thiosulfate and 2!15 mL
of water, respectively. The combined organic layers were
dried over anhydrous Na2SO4. Filtration and evaporation of
the solvent under rotary evaporator gave the corresponding
alkene. In the case of low boiling point alkenes (Table 3,
entries 1–3, 5 and 6) liquid air cooled, bulb-to-bulb
distillation was used for purification. The spectral data of
the produced alkenes (3-i-propopoxy-propene, diallyl ether,
3. Experimental
3.1. General
Chemicals were either prepared in our laboratory or were
purchased from Fluka and Merck companies. The purity
determination of the products was accomplished by GC on a
Shimadzu model GC-14A instrument or by TLC on silica
gel polygram SIL G/UV 254 plates. Mass spectra were run
on a Shimadzu GC-Mass-QP 1000 EX at 20 eV. The IR
spectra were recorded on a Perkin-Elmer 781 spectro-
photometer. The NMR spectra were recorded on a Bruker
Avance DPX 250 MHz spectrometer using tetramethyl-
silane as internal standard.
1-hexene,
allyloxy
benzene,
3-chloro-propene,
cyclohexene, styrene, allyl methacrylate) were compared
to those of authentic samples.20
Acknowledgements
We gratefully acknowledge the support of this study by the
Management and Programming Organization of Iran and
Shiraz University Research Council.
3.1.1. General procedure for the conversion of epoxides
to b-bromoformates by Silphos [PCl3Kn(SiO2)n]/Br2 or
NBS in DMF. To a heterogeneous solution containing 1.5 g
of Silphos [PCl3Kn(SiO2)n] in 5 mL of dry DMF at 0 8C
1.4 mmol (0.07 mL) bromine or 0.25 g of NBS was added.
1.0 mmol of the epoxide was added after 5 min. The
progress of the reaction was monitored by TLC and GC
analysis. The epoxide disappeared in less than 10 min with
formation of the corresponding b-bromoformate as the
major product and some bromohydrin. The reaction mixture
was stirred until the complete conversion of the bromo-
hydrin to its corresponding b-bromoformate. The reaction
mixture was then filtered to separate the Silphos-oxide. The
filtrate was poured into saturated brine and the product was
extracted by 2!30 mL of ether. The organic layer was
washed with 2!20 mL of an aqueous solution of 10%
sodium thiosulfate and 2!15 mL of water, respectively.
The combined organic layers were dried over anhydrous
Na2SO4. Filtration and evaporation of the solvent under
rotary evaporator gave the corresponding b-bromoformate.
The obtained b-bromoformates were identified by compari-
son of their spectral data with those reported in the
literature.9 The spectral data of formic acid 1-bromo-
methyl-2-phenoxy-ethyl ester as a typical product is as
follows: IR (neat): 3430, 3075, 3060, 3035, 2925, 2867,
References and notes
1. See some of the latest publications: (a) Firouzabadi, H.;
Iranpoor, N.; Jafarpour, M. Tetrahedron Lett. 2005, 46,
4107–4110. (b) Surendra, K.; Krishnaveni, N. S.; Rao,
K. R. Tetrahedron Lett. 2004, 45, 6523–6526. (c)
Kaboudin, B.; Norouzi, H. Tetrahedron Lett. 2004, 45,
1283–1285. (d) Ollevier, T.; Lavie-Compin, G. Tetrahedron
Lett. 2004, 45, 49–52. (e) Yadav, J. S.; Reddy, B. V. S.;
Reddy, Ch. S. Tetrahedron Lett. 2004, 45, 1291–1293. (f)
´
Harfouche, J.; Herault, D.; Tommasino, M. L.;
Pellet-Rostaing, S.; Lemaire, M. Tetrahedron: Asymmetry
2004, 15, 3413–3418. (g) Tamami, B.; Kolahdoozan, M.
Tetrahedron Lett. 2004, 45, 1535–1537. (h) Ramos, V. D.;
Derouet, D.; Visconte, L. L. Y. Polym. Test. 2003, 22,
297–304. (i) Yoo, S. K.; Han, J. H.; Lee, S. J.; Ryu, J. Y.;
Kim, C.; Jin, S. W.; Kim, Y.; Nam, W. Inorg. Chem.
Commun. 2003, 6, 1148–1151. (j) Derouet, D.; Cauret, L.;
Brosse, J. C. Eur. Polym. J. 2003, 39, 671–686.
2. For reviews, see: (a) Sander, M. Chem. Rev. 1966, 66,
297–339. (b) Smith, J. C. Synthesis 1984, 629–656.
1711, 1594, 1487, 1234, 1140, 751 cmK1 1H NMR
;
(250 MHz, CDCl3): d (ppm)Z8.10 (s, 1H), 7.15–7.28 (m,
2H), 6.80–6.90 (m, 3H), 5.31 (m, 1H), 4.07–4.17 (m, 2H),
3.52–3.64 (m, 2H); 13C NMR (63 MHz, CDCl3); d (ppm)Z
160.1, 157.9, 129.7, 122.0, 115.1, 70.7, 66.8, 30.0; MS
(20 eV), m/e (%): 260 (4), 258 (4), 167 (96.2), 165 (100),
133 (23.5), 94 (32.3), 57 (31.4). Anal. Calcd for
C10H11BrO3: C, 46.36; H, 4.28. Found: C, 46.47, H, 4.17.
3. (a) Rosewsky, A. Heterocyclic Compounds with Three
and Four Membered Rings, Part I; Interscience:
New York, 1964; Chapter 1. (b) Sexton, A. R.; Britton,
E. C. J. Am. Chem. Soc. 1948, 70, 3606–3607. (c) Gilman,
H.; Fullhart, L. J. Am. Chem. Soc. 1949, 71, 1478–1481.
(d) Bordwell, F. G.; Anderson, H. M. J. Am. Chem. Soc.
1953, 75, 495–496. (e) Goodman, L.; Benitez, A.; Baker,
B. R. J. Am. Chem. Soc. 1958, 80, 1680–1687. (f)
Bridger, R. F.; Russel, R. R. J. Org. Chem. 1960, 25,
863–866. (g) Christensen, B. G.; Strachan, R. G.; Trenner,
N. R.; Arison, B. H.; Hir Schmann, R.; Chemerds, J. M. J.
Am. Chem. Soc. 1960, 82, 3995–4000. (h) Brown, H. C.;
Yoon, N. M. J. Am. Chem. Soc. 1966, 88, 1464–1472.
(i) Sander, M. Chem. Rev. 1966, 66, 297–339. (j)
Izydore, R. A.; Ghirardelli, G. R. J. Org. Chem. 1973,
3.1.2. General procedure for the conversion of epoxides
to alkenes by Silphos [PCl3Kn(SiO2)n]/I2 in DMF. To
a heterogeneous solution containing 1.0 g of Silphos
[PCl3Kn(SiO2)n] in 3 mL of dried DMF at room temperature
2.0 mmol (0.5 g) of iodine was added. 1.0 mmol of the
epoxide was added after 5 min. The progress of the reaction
was monitored by TLC and GC analysis. The reaction

N. Iranpoor et al. / Tetrahedron 62 (2006) 1823–1827
1827
38, 1790–1793. (k) Norton, J. R.; Shenton, K. E.;
Schwartz, J. Tetrahedron Lett. 1975, 51–54. (l) Brown,
H. C.; Krishnamurthy, S. Tetrahedron 1979, 35, 567–607.
4. (a) Iranpoor, N.; Mohammadpour Baltork, I. Synth.
Commun. 1990, 20, 2789–2797. (b) Iranpoor, N.;
Mohammadpour Baltork, I.; Shiriny, F. Tetrahedron 1991,
47, 9861–9866. (c) Iranpoor, N.; Mohammadpour
Baltork, I. Tetrahedron Lett. 1990, 31, 735–738. (d)
Iranpoor, N.; Owji, J. Tetrahedron 1991, 47, 149–154. (e)
Safavi, A.; Iranpoor, N.; Fotuhi, L. Bull. Chem. Soc. Jpn.
1995, 68, 2591–2594. (f) Iranpoor, N.; Tarrian, T.;
Movahedi, Z. Synthesis 1996, 1473–1476. (g) Iranpoor,
N.; Kazemi, F. Tetrahedron 1997, 53, 11377–11382. (h)
Iranpoor, N.; Tamami, B.; Niknam, K. Can. J. Chem. 1997,
75, 1913–1919. (i) Iranpoor, N.; Shakarriz, M.; Shiriny, F.
Synth. Commun. 1998, 28, 347–366. (j) Katsuki, H.;
Shimanouchi, T.; Ohshima, R.; Fujiwara, S. Teterahedron
1998, 54, 2709–2722. (k) Skupin, R.; Haufe, G. J. Fluorine
Chem. 1998, 92, 157–165. (l) Prestat, G.; Baylon, C.;
Heck, M.-P.; Mioskowski, C. Tetrahedron Lett. 2000, 41,
3829–3831. (m) Iranpoor, N.; Adibi, H. Bull. Chem. Soc.
Jpn. 2000, 73, 675–680. (n) Salomon, C. J. Synlett 2001,
65–68. (o) Kamal, A.; Khana, G. B. R. Tetrahedron:
Asymmetry 2001, 12, 405–410. (p) Tamami, B.; Mahdavi,
H. Tetrahedron Lett. 2001, 42, 8721–8724. (q)
I. M.; Lee, J. B. M.; Matough, F. S. Chem. Lett. 1969,
1017–1018. (g) Arain, R. A.; Hargreaves, M. K. J. Chem.
Soc. C 1970, 67–70. (h) Sonnet, P. E.; Oliver, J. E. J. Org.
Chem. 1976, 41, 3279–3284. (i) Hrubiec, R. T.; Smith, M. B.
J. Org. Chem. 1984, 49, 431–435.
6. (a) Hanack, M.; Auchter, G. J. Am. Chem. Soc. 1985, 107,
5238–5245. (b) Sandr, J.; Viala, J. Synth. Commun. 1992, 22,
2945–2948. (c) Machinek, R.; Luttke, W. Synthesis 1975,
255–256. (d) Hodge, P.; Khoshdel, E. J. Chem. Soc., Perkin
Trans. 1 1984, 195–198.
7. (a) Heer, M. E.; Johnson, R. A. J. Org. Chem. 1972, 37,
310–312. (b) Boeckman, R. K., Jr.; Ganem, B. Tetrahedron
Lett. 1974, 11, 913–916. (c) Barluenga, J.; Campos, P. J.;
Gonzalez-Nunez, E.; Asensio, G. Synthesis 1985, 426–428.
8. Caputo, R.; Ferreri, C.; Palumbo, G. Synth. Commun. 1987, 17,
1629–1636.
9. Iranpoor, N.; Firouzabadi, H.; Chitsazi, M.; Jafari, A. A.
Tetrahedron 2002, 58, 7037–7042.
10. Charette, A. B.; Boezio, A. A.; Janes, M. K. Org. Lett. 2000, 2,
3777–3779.
˚
11. Arstad, E.; Barrett, A. G. M.; Hopkins, B. T.; Kobberling, J.
¨
Org. Lett. 2002, 4, 1975–1977.
12. Yoakim, C.; Guse, I.; O’Meara, J. A.; Thavonekham, B.
Synlett 2003, 473–476.
13. Charette, A. B.; Janes, M. K.; Boezio, A. A. J. Org. Chem.
2001, 66, 2178–2180.
Sartillo-Piscil,
F.;
Quintero,
L.;
Villegas,
C.;
´
Santacruz-Juarez, E.; Parrodi, C. A. D. Tetrahedron Lett.
2002, 43, 15–17. (r) Chandrasekhar, S.; Reddy, Ch. R.;
Babu, N.; Chandrasekhar, G. Tetrahedron Lett. 2002, 43,
3801–3803. (s) Tamami, B.; Mahdavi, H. React. Funct.
Polym. 2002, 51, 7–13. (t) Tamami, B.; Mahdavi, H.
Tetrahedron Lett. 2002, 43, 6225–6228. (u) Mirkhani, V.;
Tangestaninejad, S.; Yadollahi, B.; Alipanah, L. Tetrahe-
dron 2003, 59, 8213–8218. (v) Sharghi, H.; Nasseri, M. A.;
Hassani Nejad, A. J. Mol. Catal. A: Chem. 2003, 206,
53–57. (w) Fox, D. L.; Robinson, A. A.; Frank, J. B.;
Salvatore, R. N. Tetrahedron Lett. 2003, 44, 7579–7582. (x)
Moghadam, M.; Tangestaninejad, S.; Mirkhani, V.;
Shaibani, R. Tetrahedron 2004, 60, 6105–6111. (y)
Kamal, A.; Adil, S. F.; Arifuddin, M. Ultrason. Sonochem.
2005, 12, 429–431.
14. Srivastava, R. R.; Collibee, S. E. Tetrahedron Lett. 2004, 45,
8895–8897.
15. Iranpoor, N.; Firouzabadi, H.; Jamalian, A.; Kazemi, F.
Tetrahedron 2005, 61, 5699–5704.
16. Iranpoor, N.; Firouzabadi, H.; Jamalian, A. Synlett 2005,
1447–1449.
17. Iranpoor, N.; Firouzabadi, H.; Jamalian, A. Tetrahedron Lett.,
2005, 46, 7963–7966.
18. (a) Kraus, G. A.; Thomas, P. J. J. Org. Chem. 1998, 53,
1395–1397. (b) Johnson, W. S.;Plummer,M. S.; PullaReddy, S.;
Bartlett, W. R. J. Am. Chem. Soc. 1993, 115, 515–521.
19. Some of the more recent publications are: (a) Gable, K. P.;
Brown, E. C. Synlett 2003, 2243–2244. (b) Patra, A.;
Bandyopadhyay, M.; Mal, D. Tetrahedron Lett. 2003, 44,
2355–2357. (c) Gable, K. P.; Brown, E. C. Organometallics
2000, 19, 944–946. (d) Antonioletti, R.; Bovicelli, P.;
Fazzolari, E.; Righi, G. Tetrahedron Lett. 2000, 41,
9315–9318. (e) Righi, G.; Bovicelli, P.; Sperandio, A.
Tetrahedron 2000, 56, 1733–1737.
5. (a) Horner, L.; Oediger, H.; Hofmann, H. Liebigs Ann. Chem.
1959, 626, 26–34. (b) Wiley, G. A.; Hershkowiz, R. L.; Rein,
B. M.; Chung, B. C. J. Am. Chem. Soc. 1964, 86, 964–965.
(c) Wiley, G. A.; Rein, B. M.; Hershkowitz, R. L.
Tetrahedron Lett. 1964, 2509–2513. (d) Kaplan, L. J. Org.
Chem. 1966, 31, 3454. (e) Schaefer, J. P.; Weinberg, D. S.
J. Org. Chem. 1965, 30, 2635–2639. (f) Brett, D.; Downie,
20. http://www.aist.go.jp/RIODB/SDBS/cgi-bin/direct_frame_
topcgi?langZeng.